Water heater



FIG. 1 is a front perspective view of a water heater showing my new design;

FIG. 2 is a top plan view;

FIG. 3 is a right side elevation view;

FIG. 4 is a right side elevation; and,

FIG. 5 is a bottom plan view.

In the drawings, the broken lines depict environmental subject matter only and form no part of the claimed design. 

The ornamental design for a water heater, as shown and described. 